Self-servo-write using ramp-tracks

ABSTRACT

Systems and techniques relating to writing servo information on a machine-readable medium. A technique includes forming servo information using a band of ramp-tracks generated based on a mechanical characteristic of a storage device. This can involve writing the band of ramp-tracks, including an embedded timing reference, to a machine-readable medium, and writing the servo information to the machine-readable medium using the band of ramp-tracks, including the embedded timing reference. An apparatus can include a self-servo-write (SSW) controller configured to direct writing of a band of ramp-tracks to a machine-readable medium based on a given rotational relationship between the machine-readable medium and a transducer. The SSW controller includes an SSWCLK generator, an angular position generator, a ramp-track pattern generator, and a servo wedge window period generator. The apparatus can be implemented as an integrated circuit device (e.g., a silicon device), a read/write channel, a disk drive, or combinations of these.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of thepriority to U.S. patent application Ser. No. 11/030,619 filed Jan. 5,2005 and entitled “Self-Servo-Write Using Ramp-Tracks”, which claims thebenefit of the priority of U.S. Provisional Application Ser. No.60/588,832, filed Jul. 15, 2004 and entitled “Self-Servo-Write MethodUsing Multiple Bands of Ramp-Tracks”, and of U.S. ProvisionalApplication Ser. No. 60/588,833, filed Jul. 16, 2004 and entitled“Self-Servo-Write Method Using Multiple Bands of Ramp-Tracks”; thisapplication is also related to U.S. patent application Ser. No.10/799,474, filed Mar. 11, 2004, and entitled “DISK SERVO PATTERNWRITING”.

TECHNICAL FIELD

The present disclosure describes systems and techniques relating toservos and writing disk servo information, for example, systems andtechniques for post-assembly, self-servowriting a magnetic recordingdisk.

BACKGROUND

In magnetic-medium-based storage devices, data is typically stored oncircular, concentric tracks on a magnetic disk surface. A read-writehead retrieves and records data on the magnetic layer of a rotating diskas it flies on a cushion of air over the disk surface. When retrievingdata, magnetic field variations are converted into an analog electricalsignal, the analog signal is typically amplified, converted to a digitalsignal and interpreted. To guarantee the quality of the informationsaved on and read back from the disk, the read-write head should be veryaccurately positioned at the center of the track during both writing andreading. Frequently, a closed-loop servo system, driven by servoinformation embedded in a dedicated portion of every track of therecording surface, is used to accurately position the head and followthe track.

The servo information defines the position of the data tracks and thusshould be written with great accuracy in order for a head servo systemto operate properly. Typically, the servo information is written on eachsurface as a radially extending set of spokes or wedges. The portion ofa servo wedge at a particular track location may contain a sync field,an index mark, a gray coded track number, and two or morefine-positioned offset bursts configured in an echelon across the track.Head positioning relative to a track center can be determined andcorrected, if necessary, by reading and noting the respective amplitudesand timings of the offset bursts.

Traditionally, a machine called a servo writer is used to write theembedded servo information on the disk surface. Commonly, a servo writeruses a large, massive granite base to minimize the effects of vibration.The servo writer can also use precision fixtures to hold the targetdrive, a precision, laser-interferometer-based actuator arm positioningmechanism to place the arms radially with respect to the axis ofrotation of the disks in the drive, and an external clock head toposition the servo wedges in time. Present servo writers are typicallylarge and expensive, and as the typical track density increases, theservo writing time also increases, which can create a bottleneck in thedisk drive manufacturing process at the servo writer station.

Various attempts have been made to reduce usage of such servo writers.For example, some servo writing techniques have used a servo writer togenerate high quality seed wedges, from which additional servo wedgescan be generated by the disk drive itself using propagation self-servowrite techniques. Other approaches have tried to eliminate thetraditional servo writer altogether by pre-writing the disk with a lowfrequency reference pattern. Yet another approach has been to attempt anincrease in throughput per servo writer by writing a spiral servopattern on the disk, from which servo wedges can be generated by thedisk drive itself.

SUMMARY

The present disclosure includes systems and techniques relating towriting servo information on a machine-readable medium. According to anaspect of the described systems and techniques, a technique includesforming servo information using a band of ramp-tracks generated based ona mechanical characteristic of a storage device. This can involvegenerating a timing reference signal based on a given rotationalrelationship between a machine-readable medium and a transducer; writingthe band of ramp-tracks, including an embedded timing reference, to themachine-readable medium based on the generated timing reference signal;and writing the servo information to the machine-readable medium usingthe band of ramp-tracks, including the embedded timing reference.

The mechanical characteristic can be an electro-mechanicalcharacteristic, and writing a ramp-track can involve operating a headand spindle motor control assembly under an open-loop condition for ashort time duration such that the ramp-track spans less than half adistance from an inner diameter to an outer diameter of themachine-readable medium. Writing the servo information can involvewriting a first portion of final servo information to themachine-readable medium using the band of ramp-tracks, and writing asecond portion of final servo information to the machine-readable mediumusing the first portion of final servo information.

Writing the second portion of final servo information can involve,iteratively, writing a next band of ramp-tracks using a previouslywritten portion of the final servo information as a reference, andwriting a next portion of the final servo information using a previouslywritten band of ramp-tracks as a reference. Writing a ramp-track caninvolve initiating a Voice-Coil Motor (VCM) ramping process from apreset angular position using a previously calibrated VCM currentprofile, where the VCM ramping process involves: accelerating a VCMactuator to a target radial velocity in a first target amount of time,and writing the ramp-track during a second target amount of time whilemaintaining the target radial velocity.

Writing the bands of ramp-tracks can involve writing overlapping,staggered bands of ramp-tracks such that ramps from one band do notintersect with ramps from a previous band. Writing the portions of thefinal servo information can involve extending a servo track zone past anedge of a corresponding ramp-track zone to prevent intersection oframp-tracks from one ramp-track zone with ramp-tracks from a previousramp-track zone.

Generating the timing reference signal can involve selecting as aninitial index reference a Back Electromotive Force (BEMF) pulse producedby the machine-readable medium rotating at a constant angular velocitywith the transducer located at a hard stop position and aself-servo-write clock locked to spindle speed. Generating the timingreference signal can involve: spinning the machine-readable medium to aconstant angular velocity, moving the transducer to a hard stopposition, locking a self-servo-write clock (SSWCLK) to spindle speed,writing a timing track to the machine-readable medium, and locking theSSWCLK to the timing track.

Writing the timing track can involve writing two or more sync-bitpatterns in the timing track. Writing the timing track can involve usinga Manchester (biphase) code in writing the two or more sync-bit patternsin the timing track. Writing the band of ramp-tracks can involve writingtwo or more sync-bit patterns in the band of ramp-tracks. Writing theband of ramp-tracks can involve using a Manchester (biphase) code inwriting the two or more sync-bit patterns in the band of ramp-tracks.

Ramp-track slope can be measured as a function of write head trackwidth, and a radial stepping size can be adjusted based on thismeasuring to facilitate writing of uniformly spaced servo tracks.Additionally, the disclosed techniques can be implemented using asoftware program operable to cause a storage device to perform theoperations.

According to another aspect, an apparatus can include a self-servo-writecontroller configured to direct writing of a band of ramp-tracks to amachine-readable medium based on a given rotational relationship betweenthe machine-readable medium and a transducer, where the self-servo-writecontroller includes a self-servo-write clock (SSWCLK) generatorconfigured to be locked to spindle speed, an angular position generatorresponsive to the SSWCLK generator, a ramp-track pattern generatorresponsive to the SSWCLK generator, and a servo wedge window periodgenerator responsive to the angular position generator.

The self-servo-write controller can further include: a write protectcomponent responsive to the servo wedge window period generator, async-bit component configured to identify sync-bits in a readbackwaveform, and a waveform amplitude demodulator configured to measureramp-track shape. The sync-bit component can include a sync-bit patterndetector and a timestamp circuit configured to detect locations ofsync-bits relative to rotation angle. Moreover, the self-servo-writecontroller can further include a timestamp circuit configured to measureBack Electromotive Force (BEMF) edges in terms of angular position.

The ramp-track pattern generator can be configured to produce multiplesync-field patterns and be configured to be used in writing bothramp-tracks and an initial timing track. The transducer can include awrite element and a read element having a radial offset from each other.Furthermore, the SSWCLK generator can be configured to be controlled bya programmable processor, and the angular position generator can includemultiple modulo counters.

The apparatus can be implemented in various devices and storage systems,including being implemented as an integrated circuit device (e.g., asilicon device), a read/write channel, a disk drive, or combinations ofthese. Moreover, the disclosed subject matter, including the functionaloperations described in this specification, can be implemented inelectronic circuitry, or in computer hardware, firmware, software, or incombinations of them, such as the structural means disclosed in thisspecification and structural equivalents thereof.

Thus, an apparatus can include self-servo-write means for directingwriting of a band of ramp-tracks to means for recording machineinformation, based on a given rotational relationship between the meansfor recording and transducer means for interfacing with the means forrecording. The self-servo-write means can include means for producing aself-servo-write clock (SSWCLK) locked to spindle speed, means fordetermining angular position, means for producing a ramp-track pattern,and means for setting a servo wedge window period.

The self-servo-write means can further include: means for asserting awrite protect signal responsive to the means for setting the servo wedgewindow period, means for identifying sync-bits in a readback waveform,and means for demodulating a waveform amplitude and for measuringramp-track shape. The means for identifying sync-bits can includesync-bit pattern detection and timestamp means for detecting locationsof sync-bits relative to rotation angle. Moreover, the self-servo-writemeans can further include means for measuring BEMF edges in terms ofangular position.

The means for producing the ramp-track pattern can include means forproducing multiple sync-field patterns and means for providingsync-field patterns during writing of both ramp-tracks and an initialtiming track. The transducer means can include means for writinginformation and means for reading information with a radial offset.Furthermore, the means for producing SSWCLK can include means forreceiving control information from processor means for programmingdevice operations, and the means for determining angular position caninclude multiple modulo means for counting.

The described systems and techniques can result in improvedself-servowriting in storage devices, enabling post-assembly,self-servowriting of a magnetic recording disk that has been left blankduring construction of the disk drive. Ramp-tracks can be written to arecording disk with sufficient density to provide high quality positionand timing information, without the ramp tracks intersecting each other.A band of ramp-tracks can be written starting from a hard-stop positionin a fully assembled disk drive, and the band of ramp-tracks can then beused as a seed from which servo information can be written to the disk.

A read-write head can coast at a well known radius (e.g., the innerdiameter or outer diameter), and a ramp-track can be written during ashort period of time after this coasting, the read-write head beingmoved a small amount of time under an open-loop condition. A set of ramptracks written in this manner can then be used as a bootstrap positionfor writing servo information, including potentially writing multiplesets of ramp-tracks across the surface of the disk. The open-loop drivecondition can be kept as short as possible during the writing of theramp-tracks. For the bands of ramp-tracks written after the first band,the head can be positioned on a previously written servo track close tothe edge of the previous band. Additional benefits can also be obtainedby placing the head many tracks inside the edge of the last writtenservo track band and relying on closed-loop control to move/accelerateto a desired velocity before releasing to open-loop, non-drive coasting.Moreover, ramp slope measurements can be performed to facilitategeneration of uniformly spaced servo tracks.

Details of one or more implementations are set forth in the accompanyingdrawings and the description below. Other features, objects andadvantages may be apparent from the description and drawings, and fromthe claims.

DRAWING DESCRIPTIONS

FIG. 1 is a block diagram showing an example magnetic-media disk drivethat employs self-servo-write using ramp-tracks.

FIG. 2 shows a process of self-servowriting.

FIG. 3 shows a process of generating a timing reference signal based ona given rotational relationship between a blank disk and a transducer.

FIG. 4 shows a process of writing a band of ramp-tracks and writingservo information using a band of ramp-tracks.

FIGS. 5-6 show a process of writing servo information using a band oframp-tracks.

FIG. 7 shows an example blank disk.

FIG. 8 shows a cutaway view of the disk and read head from FIG. 7.

FIG. 9 shows the disk from FIG. 7 after a timing track has been written.

FIG. 10 shows the disk from FIG. 9 after a first set of ramp-tracks havebeen written.

FIG. 11 shows the disk from FIG. 10 after a first portion of the finalservo wedges have been written.

FIG. 12 shows the disk from FIG. 11 after a second set of ramp-trackshave been written in an overlapped and staggered fashion.

FIG. 13 shows the disk from FIG. 12 after a second portion of the finalservo wedges have been written.

FIG. 14 shows the disk from FIG. 13 after all the ramp-tracks and finalservo wedges have been written.

FIG. 15 is a block diagram showing an example ramp-trackself-servo-write controller.

FIG. 16 is a block diagram showing another example ramp-trackself-servo-write controller.

FIG. 17 shows example timing of a sub-wedge counter and a wedge-counterwith reference to an index pulse.

FIG. 18 shows example delays and windows generator timing waveforms.

FIG. 19 shows an example Manchester (biphase) encoded write waveform.

FIG. 20 shows an example timing track pattern.

FIG. 21 shows an example high resolution timestamp circuit.

FIG. 22 shows an example of ramp-track writing timing waveform.

FIG. 23 shows an expanded view of example ramp-tracks.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The systems and techniques described herein can be implemented as one ormore devices, such as one or more integrated circuit (IC) devices, in astorage device. For example, they can be implemented in a read/writechannel transceiver device suitable for use in a magnetic recordingsystem. In general, a storage device employing self-servo-write asdescribed includes a machine-readable medium (e.g., a magnetic-mediadisk) and a transducer (e.g., a medium read element and a medium writeelement, which can be integrated into a single read-write head).

FIG. 1 is a block diagram showing an example magnetic-media disk drivethat employs self-servo-write using ramp-tracks. The disk drive includesa head-disk assembly (HDA) 100 and drive electronics 150 (e.g., aprinted circuit board assembly (PCBA) with semiconductor devices). TheHDA 100 includes one or more disks 110 mounted on an integrated spindleand motor assembly 115. The spindle and motor assembly 115 rotates thedisk(s) 110 under read-write head(s) connected with a head assembly 120in the HDA 100. The disk(s) 110 can be coated with a magnetically hardmaterial (e.g., a particulate surface or a thin-film surface) and can bewritten to, or read from, a single side or both sides of each disk.

A head 132 on an arm 130 can be positioned as needed to read data on thedisk. A motor, such as a voice coil motor (VCM), can be used to positionthe head over a desired track. The arm 130 can be a pivoting or slidingarm and can be spring-loaded to maintain a proper flying height for thehead 132 in any drive orientation. A closed-loop head positioning systemcan be used.

The HDA 100 can include a preamp/writer 140, where head selection andsense current value(s) can be set. The preamp/writer 140 can amplify aread signal before outputting it to signal processing circuitry 170. Thesignal processing circuitry 170 can include a read signal circuit, aservo signal processing circuit, and a write signal circuit.

Signals between the HDA 100 and the drive electronics 150 can be carriedthrough a flexible printed cable. A controller 180 can direct a servocontroller 160 to control mechanical operations, such as headpositioning through the head assembly 120 and rotational speed controlthrough the motor assembly 115. The controller 180 can be one or more ICchips (e.g., a combo chip), which can include read/write channel signalprocessing circuitry 170. The controller 180 can be a microprocessor anda hard disk controller. The drive electronics 150 can also includevarious interfaces, such as a host-bus interface, and memory devices,such as a read only memory (ROM) for use by a microprocessor, and arandom access memory (RAM) for use by a hard disk controller. Theread/write channel 170 can include error correction circuitry.

The disk drive includes a self-servo-write controller that causes servoinformation to be written on the machine-readable medium as described.The self-servo-write controller can be integrated into a device, such asa read/write channel transceiver device (e.g., the read/write channel170) suitable for use in a magnetic recording system. Theself-servo-write controller can be composed of multiple sets ofcoordinating circuitry and can be integrated with the componentsdescribed above or organized into a separate component of a disk drive.For example, the self-servo-write controller can be integrated into thecontrollers 160, 180, the read/write channel 170, the preamp/writer 140,or various combinations of these components (e.g., the components 160,170, 180 can all be combined into a single integrated circuit).

FIG. 2 shows a process of self-servowriting. A timing reference signalis generated based on a given rotational relationship between amachine-readable medium and a transducer at 210. A band of ramp-tracks,including an embedded timing reference, is written to themachine-readable medium based on the generated timing reference signalat 220. Servo information is written to the machine-readable mediumusing the band of ramp-tracks, including the embedded timing reference,at 230.

Detailed examples of these operations in the context of a magnetic-mediadisk are described below. However, alternative embodiments are alsopossible. For example, the initial set of ramp-tracks can be used as aseed for propagation self servo write (SSW) techniques. In thisapproach, the propagation SSW techniques can be used to propagate theservo tracks all the way to the other end of the disk, such as when theread-write head has a write element that is always ahead of the readelement in the direction of propagation. Thus, in some implementations,only a single set of ramp-tracks need be written.

FIG. 3 shows a process of generating a timing reference signal based ona given rotational relationship between a blank disk and a transducer. Ablank disk can be spun to a constant angular velocity at 310. The headcan be moved to a hard stop position at 320. The description belowassumes the hard stop position is the inner diameter (ID), but thesystems and techniques described are equally applicable to using theouter diameter (OD) as the initial hard stop position. Aself-servo-write clock (SSWCLK) can be locked to spindle speed at 330.

A timing track can then be written at 340, and the SSWCLK reference canbe switched from the spindle reference to signals from the referencetiming track at 350. These operations are fully optional, but may bevery useful for heads with a write element further away from the hardstop than the read element (i.e., heads with a positive radial offsetfor write-read elements).

The written timing track contains a timing reference. For example,writing the timing track can involve writing two or more sync-bitpatterns in the timing track, which can include using a Manchester(biphase) code, as described further below. The head can be moved awayfrom the hard stop after writing the timing track, and the head's readelement can then be servo-locked onto one edge of the timing referencetrack. In some implementations, writing the initial timing track neednot be done, such as when the read-write elements on the head have nearzero offset at the hard stop position.

An initial index reference can be determined at 360. This can involveselecting as the initial index reference one of the Back ElectromotiveForce (BEMF) pulses around one revolution of the disk when no timingtrack is used. When SSWCLK is locked to a timing track, this can involveselecting one of the timing marks on the timing track to be used as theinitial index reference.

With the initial index reference determined, an angular positionreference can be provided at 370. For example, one or more countersrunning on SSWCLK can be set up to provide the angular positionreference. These counter(s) can include two modulo counters. A firstsuch modulo counter can be a sub-wedge modulo counter whose modulo valueis set to half the target number of clocks between two consecutive servowedges (i.e., a half wedge spacing scheme). Other spacing schemes arealso possible. A second such modulo counter can be a wedge-count modulocounter whose count keep tracks of the half-wedge numbers. For example,the wedge-count modulo counter can update its value when the sub-wedgemodulo counter wraps its value around.

In addition, providing the angular position reference can involveperforming a one time initialization of the angular position referencecounters right after an arrival of the initial index reference. Theindex reference can then be relocated to a unique once-around-the-diskcount position defined by the angular position reference counters at380. For example, the index reference can be reset to the zero countposition of both modulo counters, if desired.

Final wedge window locations can be set up at 390. For example, this canbe defined as a fixed length region initiated when the sub-wedge modulocount value hits a preset number, and when the wedge-count modulocounter is on one of an even or odd number.

FIG. 4 shows a process of writing a band of ramp-tracks and writingservo information using a band of ramp-tracks. A ramp-track patterngenerator running on SSWCLK can be set up at 410. The ramp-track patterncan include a mostly sync-field pattern with sync-bits uniformlyinterspersed. The sync-bits need not be all of the same type. Having atleast two different types of sync-bits can be desirable: one to provideindex referencing, the other for general timing marks. Moreover, havinga 3rd type of sync-bits can provide additional robustness in the system.Such sync-bits can be placed once every wedge distance, right inside ornear the region defined by the wedge window position.

A VCM ramping process can be initiated from a preset angular positionusing a previously calibrated VCM current profile at 420. The previouslycalibrated VCM current profile can be based on a study made using thesame type of mechanical component as used in the disk drive. A VCMactuator can be accelerated to a target radial velocity in a firsttarget amount of time at 430. The ramp-track can then be written duringa second target amount of time while maintaining the target radialvelocity at 440. The write head can be turned on during this secondperiod of time with write-protect turn-off during the wedge-windowperiod. The VCM can then be retracted.

While additional ramp-tracks remain to be written at 450, the remainingramp-tracks can be written in the same manner as above, starting fromdifferent but equally spaced angular positions. In each case, writingthe ramp-track can involve operating a head and spindle motor controlassembly under an open-loop condition for a short time duration, asshown and described.

Once the full set of ramp-tracks have been written, a portion of finalservo information can be written using the band of ramp-tracks at 460.And remaining final servo information can be written using the portionof final servo information at 470. This can involve, iteratively,writing a next band of ramp-tracks using a previously written portion ofthe final servo information as a reference, and writing a next portionof the final servo information using a previously written band oframp-tracks as a reference. In this implementation, the write-protectturn-off during the wedge-window period may be skipped during thewriting of the first set of ramp-tracks, but then used during thewriting of the remaining sets of ramp-tracks.

FIGS. 5-6 show a process of writing servo information using a band oframp-tracks. A VCM can be moved gently from near the hard stop positioninto the ramp-track region. When the read electronics have detected mostof the ramp-tracks, the VCM can be servo locked onto a fixed radialposition defined by a timing location of the ramps relative to a spindlereference at 510. The SSWCLK can be relocked to the timing referencefound on the ramp-tracks at 520. Note that the ramp-tracks and thetiming track can be written using the same pattern generator in order tominimize transient in the SSWCLK during the switch over.

Optionally, repeatable run out (RRO) cancellation can be applied to theVCM servo lock loop to minimize the repeatable component of VCM currentvariation around every revolution. The RRO cancellation used can be thatdescribed in U.S. Pat. No. 6,775,091, entitled “Repeatable run-outcompensation for disk drive”, which is hereby incorporated by reference.A servo track is written at 530. A servo track can be written inmultiple passes. For example, a servo track may require two or threepasses of different write patterns to complete the writing. This can beinitiated at every wedge window position.

While additional servo tracks remain to be written at 540, the servowriting continues. In addition, a ramp-track slope can be measured as afunction of write head track width at 550; and a radial stepping sizecan be adjusted based on this measuring to facilitate writing ofuniformly spaced servo tracks at 560. The VCM can be moved radially insuch a way as to measure the written head track width. Even when the VCMvelocity during ramp write has been previously calibrated, re-measuringthe slope of the ramps as a function of the write track head width canprovide additional accuracy.

This can result in at least two major benefits: (1) the calibrationneeded to even out residual variations during the ramp write process canbe determined, and (2) how best to step the tracks can be determinedsince how many tracks can be written may depend on the width of thewrite head instead of a fixed stepping distance due to write head widthvariations.

The head can be stepped according to a normal servo stepping requirementto write as many servo tracks as can be supported by the ramp-tracks.The measurement of the ramp-track slope and adjustment to the radialstepping size can be done at various times and need not be done betweenthe writing of each servo track as shown. Once no additional servotracks are needed, the servo wedges within the first ramp-track bandhave been completed. However, servo tracks can also be written beyondthe end of the ramp-tracks as discussed further below.

A check can be made regarding whether additional ramp-tracks are neededat 570. While additional ramp-tracks are needed, the process continues.Once all the servo tracks have been written to disk, any additionaloperations can be performed at 580. For example, various clean up and/orverification operations can be performed, such as doing read/write onthe entire disk surface to certify the disk.

Performing the self-servo writing process can involve using overlappingramp-tracks or not. In a non-overlapping approach, a servo track zonecan be extended past an edge of a corresponding ramp-track zone at 590.This can be done as part of the self-servo writing process in order toprevent intersection of ramp-tracks from adjacent ramp-track zones.Alternatively, writing the bands of ramp-tracks can involve writingoverlapping, staggered bands of ramp-tracks at 590, such that ramps fromone band to a next band do not intersect. In general, the next set oframp-tracks to be written cover a radial region that starts near the endof the previous set of ramp-tracks.

When the ramp-tracks are overlapped, the next set of ramps should beplaced in angular positions that ensure no intersection of the currentset of ramp-tracks with the previous set of ramp-tracks (e.g., aposition that is half way in between the previous set of ramps, as shownin FIG. 12).

When the ramp-tracks are not overlapped, the servo track zone can beextended beyond the corresponding ramp-tracks, such as by usingpropagation SSW techniques to extend the first SSW servo band. Moreover,the outer band portion of the first ramp-tracks can be erased at thesame time propagation SSW is preformed to reduce the number of extensiontracks needed. The next set of ramp-tracks can thus be written withoutany radial overlap with the first set of ramp-tracks.

In either case, the process can continue through circle-A to FIG. 6,which shows a process that repeats until the whole disk is completelyself-servo written with servo wedges.

A next set of ramp-tracks is written at 610. This can involve servolocking the VCM onto a previously written servo track. For example, theVCM can be servo locked so that the read head is positioned on apreviously written servo track near the end of the previously writtenband at a radial position=RS2. The SSWCLK reference can be switched tothe timing marks (sync-mark) in final servo wedges written in theprevious radial band, taking into account the timing offset between thesync-marks in the servo wedges and the timing marks in the previousramp-track region.

Starting from preset angular positions, the VCM actuator can beinitiated such that it moves to a constant velocity before the headexits the first ramp-track zone. This can be done using open-loopcalibrated impulse current through the VCM, or using closed loop controlduring the time the head flies over the previously written servo track.For example, in the overlapped ramp-track approach, the write head canstart moving from a predetermined radial position RW2 (as feedback frompreviously written servo tracks) before it exits the previous ramp-trackzone.

The ramp write can be terminated a fixed time later, and shortly afterthat the head can be retracted back to RS2 location. This can berepeated until all the ramp-tracks have been written. Additionally, inthe overlapped ramp-track approach, write protect gating can beperformed around the wedge window period, at least within the overlappedradial zone.

After each set of ramp-tracks is written, the next set of servo wedgesis written. The following description is given in the context of theoverlapped ramp-track approach, but the overall process is stillapplicable to the non-overlapped approach.

The VCM can be servo locked onto a previously written servo track withinthe overlapped zone at 620. Radial position as determined by the currentset of ramp-tracks can be measured at 630. The difference between theradial position defined by the servo track and the radial positiondefined by the recently written set of ramp-tracks can provide theoffset information used to continue with the self-servo-write of theservo tracks past the previously written zone without having to addressradial stitching.

The SSWCLK locking reference can be switched to the timing marks on thesecond set of ramp-tracks at 640. A dummy wedge can be written away fromthe desired wedge location at 650. The timing position of the dummywedge can then be measured relative to the timing marks on theramp-tracks at 660. This information can provide the timing offsetbetween the read and write elements. Adjustment can then be made to theSSWCLK to ensure that there is no timing coherence issue between theprevious servo tracks and the newly written servo tracks.

An RRO cancellation can be applied to the VCM servo lock loop at 670 tominimize the repeatable component of VCM current variation around everyrevolution. The servo wedges are written at 680. This can involvestepping through the radius within the current set of ramp-tracks andwriting servo wedges as described above. In addition, as before,periodic measurement of ramp-track slope and adjustment of radialstepping size can be performed at 690. The process continues, throughcircle-B to FIG. 5, until all the servo information has been written.

FIGS. 7-14 show an example of the overlapped ramp-track approach toself-servo writing. A blank disk 700 is shown in FIG. 7, with a head 720on an arm 710 positioned against a hard stop 730. FIG. 8 shows a cutawayview of the read head 720 positioned over a portion of the disk 700 froma perspective of being at the end of the read head 720 and looking backup the arm 710. ID is to the right in FIG. 8 and OD is to the left inFIG. 8.

The head 720 can include a write element 810 and a read element 820 witha positive radial offset as shown. The disk 700 can include one or morelayers. For example, the disk 700 can be a perpendicular magneticrecording (PMR) disk that includes a high permeability (“soft”) magneticunder-layer 830 between a perpendicularly magnetized thin film datastorage layer 840 and a substrate 850. Other disk writing technologiescan also be used, such as traditional longitudinal magnetic recording.

FIG. 9 shows the disk 700 after a timing track 910 has been written.FIG. 10 shows the disk 700 after a first set of ramp-tracks 1010 havebeen written. FIG. 11 shows the disk 700 after a first portion of thefinal servo wedges (e.g., wedge 1110) have been written. FIG. 12 showsthe disk 700 after a second set of ramp-tracks 1210 have been written inan overlapped and staggered fashion. FIG. 13 shows the disk 700 after asecond portion of the final servo wedges have been written. FIG. 14shows the disk 700 after all the ramp-tracks and final servo wedges havebeen written.

Thus, the multi-ramp self-servo-write scheme involves writing a set ofshort to intermediate length servo reference traces that ramp from aposition at or near a hard stop position (radius) to another radius.Each set of ramp-tracks does not extend all the way to the other side ofthe disk. For example, each set of ramp-tracks may span less than half,less than third, less than fourth, or less than eighth a distance froman inner diameter to an outer diameter of the machine-readable medium.In general, the dimensions of the ramp-tracks used can be inverselyproportional to the tolerance of the VCM control. For example, if theVCM control and spindle have a tolerance of 1%, then the ramp-tracks canspan a distance of about one hundred final servo tracks. In general, thespan of a set of ramp-tracks can be less than or equal to one thousandfinal servo tracks, less than or equal to one hundred final servotracks, or in the range of three to ninety final servo tracks.

The first set of ramp-tracks can be used to provide the position andtiming reference used for self-servo-writing of a small band of finalservo tracks and wedges. The servo-wedges written in this way cover aradial range spanned by the ramp-track zone. Then another set ofreference ramps can be written, with starting radius located on one ofthe written servo tracks to serve as the bootstrapped position. Thissecond set of reference ramps can then be used to extend the writtenservo tracks further to the outer edge of the new ramps. This processcan be continued until the whole disk is written with final servotracks.

All the electronics that perform these self-servo-write operations canbe included in the electronics that support normal drive operation, suchthat a disk drive can perform self-servo-write and self-test without theaid of additional hardware outside the HDA and PCBA.

FIG. 15 is a block diagram showing an example ramp-trackself-servo-write controller 1500. An SSWCLK generator 1510 is configuredto be locked to spindle speed and may be controllable by a processorrunning software or firmware. An angular position generator 1520 isresponsive to the SSWCLK generator 1510 and may include multiple modulocounters. A ramp-track pattern generator 1530 is responsive to theSSWCLK generator 1510 and may be configured to produce multiplesync-field patterns. A servo wedge window period generator 1540 isresponsive to the angular position generator 1520 and can runsynchronously to the disk.

The pattern generator 1530 can also be configured to be used in writingboth ramp-tracks and an initial timing track. The sync-field pattern(s)produced by the pattern generator 1530 can include uniformlyinterspersed timing marks and can use one or more types of sync-bitpatterns. Manchester (biphase) code can be used for encoding thesync-field and sync-bits. An example sync field is all “1”'s Manchesterdata bits, with a Manchester “1” defined as a 1100 NRZ (No Return toZero) pattern (each NRZ bit being one SSWCLK), and a manchester value of0 defined as a 0011 NRZ pattern. Examples of sync-bit patterns are (interms of Manchester bits): (a) 1101, (b) 1001, etc. One sync-bit patterncan be used for the index mark (which occurs once per revolution), andany additional sync-bit patterns can be used for higher frequency timingmarks.

The SSW controller 1500 can also include a sync-bit component 1550configured to identify sync-bits in a readback waveform obtained fromthe recording medium. The sync-bit component 1550 can include one ormore sync-bit pattern detectors and timestamp circuits 1552, 1554configured to detect locations of sync-bits relative to rotational angleof the recording medium. A waveform amplitude demodulator 1560 can beincluded and be configured to measure ramp-track shape as the read headcrosses the ramp-tracks. Additionally, a write protect component 1570can be included and be responsive to the servo wedge window periodgenerator 1540 and can be tied to the wedge window period.

FIG. 16 is a block diagram showing another example ramp-trackself-servo-write controller. A processor 1605 (e.g., amicroprocessor/microcontroller) can perform computations as needed usingsoftware or firmware 1607. An interface and interrupt control 1610provides an interface between the processor 1605 and other components ofthe SSW controller.

An angular position counter 1615 receives counter parameters on a line1616 and provides an index pulse on a line 1618, both coupled to theinterface and interrupt control 1610. The angular position counter 1615also provides an angular position value on a line 1617. Moreover,additional similar counters can be included in the SSW controller.

An initialization control 1620 receives an index initialization on aline 1621 and receives BEMF pulses on a line 1632 (e.g., from the motordriver). A high resolution SSWCLK generator 1625 can be controlled bythe processor 1605 and provides a clock signal to an SSWCLK line 1627.Multiple counters can be clocked by SSWCLK, running synchronously to thedisk, and can be used to define the angular position of the recordingdisk. The counters can be programmed to have a complete period coveringone revolution of the disk.

A spindle BEMF timestamper 1630 can measure the BEMF edges in terms ofthe angular position defined by the synchronous counter(s), providingthe location information of the BEMF pulses consistent with the angularposition used by the SSW processes. This timestamp circuit need not haveresolution higher than the SSWCLK period since the BEMF pulses usuallyhave larger uncertainties than one SSWCLK period.

A signal from the read head can be received on a line 1602 and providedto a servo channel 1650 and an SSW timing track detector 1655. The servochannel 1650 can provide servo gray code and Position Error Signal (PES)Demod Values to the interface and interrupt control 1610 on a line 1653(see e.g., U.S. Pat. No. 6,775,338, entitled “Digital servo channel forrecording apparatus”). The servo channel 1650 can also provide a servomark (SM) detect signal to the interface and interrupt control 1610 andto a high resolution sync-mark timestamper 1632 used to detect thelocation of sync-marks from servo wedges.

A high resolution timing mark timestamper 1634 can be used to detect thelocation of timing marks relative to the rotation angle. The resolutionshould be in a resolution substantially smaller than the period of oneSSWCLK. The SSW timing track detector 1655 can provide timing mark (TM)type information to the interface and interrupt control 1610 and also TMdetect information to both the interface and interrupt control 1610 andthe timing mark timestamper 1634.

A delays and windows generator 1640 can interact with the interface andinterrupt control 1610, a write gate mask 1660, and a timing pattern andservo wedge generator(s) 1645. Target values can be provided from theinterface and interrupt control 1610 to the delays and windows generator1640, and timing and window pulses can be provided from the delays andwindows generator 1640 to the interface and interrupt control 1610. Inaddition, a ramp WGATE signal can be provided on a line 1641 and a wedgewindow signal can be provided on a line 1642.

The write gate mask 1660 can receive a write mask enable signal on aline 1662. The write gate mask 1660 can include a write enable circuitwith programmable turn-on and turn-off time relative to disk angularposition, such as defined by the counter(s), and also a write protectcircuit tied to the wedge window period. If enabled, the write protectcircuit disables writing to the disk even during the write-enable perioddefined by the write enable circuit.

Output (WGATE) of the write gate mask 1660 can be provided to a preampcontrol. Additionally, output of a PECL (positive emitter coupled logic)driver 1665 can be provided to preamp write input pins.

FIG. 17 shows example timing of a sub-wedge counter 1710 and awedge-counter 1720 with reference to an index pulse 1730. The sub-wedgecounter 1710 and the wedge-counter 1720 combine to form an angularposition counter.

FIG. 18 shows example delays and windows generator timing waveforms. Asub-wedge counter value 1802 and a wedge-count counter value 1804 can beused in controlling writing of the ramp-tracks. As shown, asub-wedge-start-ramp 1810 and a wedge-count-start-ramp 1814 trigger aVCM-ramp pulse 1820, which starts a VCM-ramp signal 1822 lasting for aVCM-ramp-pulse-period 1824. After a ramp-write-delay 1830, a ramp WGATEsignal 1832 lasts for a ramp-write-period 1834. A wedge-window-start1812 and an even-wedge-count 1840 (a mod 2 counter) trigger awedge-window-start pulse 1842, and a wedge-window 1844 lasts for awedge-window-period 1846.

FIG. 19 shows an example Manchester (biphase) encoded write waveform. Adata pattern 1910 corresponds to Manchester (biphase) encoded bits 1920.

FIG. 20 shows an example timing track pattern, which includes an indexframe 2010 and normal frames 2020, 2030. The index frame 2010 includesan index mark portion 2012. A normal frame 2020 includes a normal timingmark portion 2022. This example timing track waveform can also be usedfor ramp-tracks.

FIG. 21 shows an example high resolution timestamp circuit. The exampleshown is for SM detect signal edge, but similar structures can be usedfor the other timestampers. A wedge-count counter value 2110 is providedto a first latch 2112. A sub-wedge counter value 2120 is provided to asecond latch 2122. An SM detect signal 2130 is provided to a fractionalsignal edge timestamp 2132, which outputs a synchronized pulse for SMdetect signal to the enable lines of the latches 2112, 2122. An output2140 provides the timestamp value.

FIG. 22 shows an example of ramp-track writing waveform timing. Aramp-track 2212 is written between an acceleration period 2210 and adeceleration period 2214. The head trajectory 2220 between a reversedacceleration period 2216 and a braking deceleration period 2218 is alsoshown. FIG. 22 also shows the timing of various signals: a VCM-rampsignal 2230, a VCM current signal 2240, a ramp-WGATE signal 2250, awedge-window signal 2260, a WGATE signal 2270, and a PECL output (topreamp writer input) signal 2280.

FIG. 23 shows an expanded view of example ramp-tracks 2310. As shown,within a wedge-window period 2320, a servo wedge 2330 can be placedbetween the ramp-tracks.

A few embodiments have been described in detail above, and variousmodifications are possible. The disclosed subject matter, including thefunctional operations described in this specification, can beimplemented in electronic circuitry, or in computer hardware, firmware,software, or in combinations of them, such as the structural meansdisclosed in this specification and structural equivalents thereof,including potentially a software program operable to cause one or moremachines to perform the operations described. It will be appreciatedthat the order of operations presented is shown only for the purpose ofclarity in this description. No particular order is required for theseoperations, and some or all of the operations may occur simultaneouslyin various implementations. Moreover, not all of the operations shownneed be performed to achieve desirable results.

Other embodiments fall within the scope of the following claims.

1. An apparatus comprising: a recording disk; a transducer configured towrite to the recording disk; and a self-servo-write controllerconfigured to cause performance of post-assembly operations comprisingwriting a band of ramp-tracks to the recording disk starting from ahard-stop position, each ramp-track spanning less than half a distancefrom an inner diameter to an outer diameter of the recording disk, andwriting servo information to the recording disk using the band oframp-tracks as a seed.
 2. The apparatus of claim 1, wherein theself-servo-write controller is configured to cause writing the servoinformation by causing operations comprising: writing a first portion ofservo information to the recording disk using the band of ramp-tracks,and writing a second portion of servo information to the recording diskusing the first portion of servo information.
 3. The apparatus of claim2, wherein the self-servo-write controller is configured to causewriting the second portion of servo information by causing operationscomprising: writing a next band of ramp-tracks using a previouslywritten portion of the servo information as a reference, and writing anext portion of the servo information using a previously written band oframp-tracks as a reference.
 4. The apparatus of claim 3, wherein theself-servo-write controller is configured to cause writing of each ofthe first portion and the next portion of the servo information byextending a servo track zone past an edge of a corresponding ramp-trackzone to prevent intersection of ramp-tracks from one ramp-track zonewith ramp-tracks from a previous ramp-track zone.
 5. The apparatus ofclaim 1, wherein the self-servo-write controller is configured to causewriting a ramp-track by initiating a Voice-Coil Motor (VCM) rampingprocess from a preset angular position using a previously calibrated VCMcurrent profile, the VCM ramping process comprising: accelerating a VCMactuator to a target radial velocity in a first target amount of time,and writing the ramp-track during a second target amount of time whilemaintaining the target radial velocity.
 6. The apparatus of claim 1,wherein the self-servo-write controller is configured to causeperformance of the post-assembly operations comprising writingoverlapping, staggered bands of ramp-tracks such that ramp-tracks fromone band do not intersect with ramp-tracks from a previous band.
 7. Theapparatus of claim 1, wherein the self-servo-write controller isconfigured to cause performance of the post-assembly operationscomprising: measuring ramp-track slope as a function of write head trackwidth; and adjusting a radial stepping size based on said measuring tofacilitate writing of uniformly spaced servo tracks.
 8. A systemcomprising: a processor; a recording disk operationally coupled with theprocessor; a transducer configured to write to the recording disk; and aself-servo-write controller configured to cause performance ofpost-assembly operations comprising writing a band of ramp-tracks to therecording disk starting from a hard-stop position, each ramp-trackspanning less than half a distance from an inner diameter to an outerdiameter of the recording disk, and writing servo information to therecording disk using the band of ramp-tracks as a seed.
 9. The system ofclaim 8, wherein the self-servo-write controller is configured to causewriting the servo information by causing operations comprising: writinga first portion of servo information to the recording disk using theband of ramp-tracks, and writing a second portion of servo informationto the recording disk using the first portion of servo information. 10.The system of claim 9, wherein the self-servo-write controller isconfigured to cause writing the second portion of servo information bycausing operations comprising: writing a next band of ramp-tracks usinga previously written portion of the servo information as a reference,and writing a next portion of the servo information using a previouslywritten band of ramp-tracks as a reference.
 11. The system of claim 10,wherein the self-servo-write controller is configured to cause writingof each of the first portion and the next portion of the servoinformation by extending a servo track zone past an edge of acorresponding ramp-track zone to prevent intersection of ramp-tracksfrom one ramp-track zone with ramp-tracks from a previous ramp-trackzone.
 12. The system of claim 8, wherein the self-servo-write controlleris configured to cause writing a ramp-track by initiating a Voice-CoilMotor (VCM) ramping process from a preset angular position using apreviously calibrated VCM current profile, the VCM ramping processcomprising: accelerating a VCM actuator to a target radial velocity in afirst target amount of time, and writing the ramp-track during a secondtarget amount of time while maintaining the target radial velocity. 13.The system of claim 8, wherein the self-servo-write controller isconfigured to cause performance of the post-assembly operationscomprising writing overlapping, staggered bands of ramp-tracks such thatramp-tracks from one band do not intersect with ramp-tracks from aprevious band.
 14. The system of claim 8, wherein the self-servo-writecontroller is configured to cause performance of the post-assemblyoperations comprising: measuring ramp-track slope as a function of writehead track width; and adjusting a radial stepping size based on saidmeasuring to facilitate writing of uniformly spaced servo tracks.
 15. Anapparatus comprising: means for recording data; means for writing to themeans for recording; and post-assembly means for self-servo-writing tothe means for recording, including means for writing a band oframp-tracks to the means for recording starting from a hard-stopposition, each ramp-track spanning less than half a distance from aninner diameter to an outer diameter of the means for recording, andmeans for writing servo information to the means for recording using theband of ramp-tracks as a seed.
 16. The apparatus of claim 15, whereinthe post-assembly means for self-servo-writing comprises means forwriting a first portion of servo information to the means for recordingusing the band of ramp-tracks, and means for writing a second portion ofservo information to the means for recording using the first portion ofservo information.
 17. The apparatus of claim 16, wherein thepost-assembly means for self-servo-writing comprises means for writing anext band of ramp-tracks using a previously written portion of the servoinformation as a reference, and means for writing a next portion of theservo information using a previously written band of ramp-tracks as areference.
 18. The apparatus of claim 17, wherein the post-assemblymeans for self-servo-writing comprises means for extending a servo trackzone past an edge of a corresponding ramp-track zone to preventintersection of ramp-tracks from one ramp-track zone with ramp-tracksfrom a previous ramp-track zone.
 19. The apparatus of claim 15, whereinthe post-assembly means for self-servo-writing comprises means forwriting a ramp-track by initiating a Voice-Coil Motor (VCM) rampingprocess from a preset angular position using a previously calibrated VCMcurrent profile, the VCM ramping process comprising: accelerating a VCMactuator to a target radial velocity in a first target amount of time,and writing the ramp-track during a second target amount of time whilemaintaining the target radial velocity.
 20. The apparatus of claim 15,wherein the post-assembly means for self-servo-writing comprises meansfor writing overlapping, staggered bands of ramp-tracks such thatramp-tracks from one band do not intersect with ramp-tracks from aprevious band.
 21. The apparatus of claim 15, wherein the post-assemblymeans for self-servo-writing comprises: means for measuring ramp-trackslope as a function of write head track width; and means for adjusting aradial stepping size based on said means for measuring to facilitatewriting of uniformly spaced servo tracks.